Magnetic recording medium

ABSTRACT

A magnetic recording medium comprising alumite made by anodic oxidation of aluminum or an aluminum alloy and comprising fine pores in which a ferromagnetic material is filled, wherein an in-plane remanence is at least 2.5 times greater than a perpendicular remanence and a magnetic recording medium of the above alumite, wherein the magnetic material is at least one material selected from the group consisting of Fe or Co, alloy mainly composed of Fe or Co, an Co or Fe containing a P element, and an alloy mainly composed of Co or Fe and containing the P element.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a magnetic recording medium, and morespecifically, to a magnetic recording medium including a magneticalumite in-plane anisotropy film.

Statement of Related Art

It is known that a magnetic alumite film in which fine pores in thealumite are filled with a magnetic metal such as Fe, Co, Ni and the likeby plating, exhibits perpendicular magnetic anisotropy because of itsshape anisotropy.

Recently, it has become possible to control the coercive force of analumite perpendicular magnetization film to 1000 Oe or less by a finepore enlarging treatment and thus the possibility of applying themagnetic alumite film to a perpendicular magnetic recording medium isincreased.

Nevertheless, since the read and write characteristics of aperpendicular magnetic recording medium (hereinafter, referred to as R/Wcharacteristics) are greatly deteriorated as the distance (spacing)between a head and a medium increases in perpendicular magneticrecording, a stable spacing of 0.05 micrometer or less is necessary tomake the best use of the intrinsic characteristics of the perpendicularmagnetic recording.

In a hard disk having a magnetic alumite film, a magnetic head isfloated about 0.3 micrometer above a medium while recording andreproduction are executed and this floating amount does not permitrecording to be sufficiently performed to the lowermost layer of themedium in a perpendicular magnetic recording. As a result, sufficientoutput cannot be obtained in reproduction and further sufficientoverwrite characteristics cannot be obtained.

Therefore, as a principle, perpendicular magnetic recording making useof a magnetic alumite film, as well as a perpendicularly magnetizedfilm, is executed using a head/medium contact type.

A CoCr or Co-CoO type perpendicular anisotropy film can provide aflexible medium such as a tape or floppy to realize the head/mediumcontact type. However, cracks easily develop in the magnetic alumitefilm when it is bent because amorphous Al₂ O₃ constituting alumite ishard and brittle, and thus it is very difficult to make a flexiblemedium using magnetic alumite film.

Because of the reason mentioned above, alumite perpendicular anisotropyfilms have a fatal drawback in that they cannot be practically used as amagnetic recording medium, although exhibiting excellent perpendicularmagnetic anisotropy.

SUMMARY OF THE INVENTION

The first object of the present invention is to provide an alumite typemagnetic recording medium exhibiting excellent R/W characteristics, evenif a magnetic head is floated about 0.15 to 0.35 micrometer above thesurface of a magnetic alumite film.

A second object of the present invention is to provide a magneticrecording medium having an in-plane anisotropy film exhibiting stableR/W characteristics.

To achieve the first object of the present invention, as shown in FIG.3, a magnetic recording medium is provided comprising an alumite layer 3made by anodic oxidation of aluminum or an aluminum alloy having finepores in which a ferromagnetic material 1 is filled, characterized inthat in-plane remanence is 2.5 times or more greater than aperpendicular remanence.

Hereinafter, "a body of magnetic material existing in each pore" isreferred to as "a magnetic particle".

To achieve the second object, the second aspect of the present inventionis to provide a magnetic recording medium comprising an in-planemagnetic anisotropy film composed of porous alumite formed on asubstrate, characterized in that anisotropy field Hk in the film planeis 100 Oe or less.

The magnetic recording medium of the present invention is preferable fora rigid disk.

A third aspect of the present invention is to use Co or Co-Ni alloycontaining Fe as a magnetic material to be filled in alumite fine poresby plating.

The magnetic recording medium having the alumite fine pores in which themagnetic material is filled by plating can be made into a longitudinalmagnetic recording medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a characteristic diagram showing the direction dependence ofin-plane magnetic characteristics of a Co-P plated alumite film ofExample 1 and a CoNi sputtered film of Comparative Example 1;

FIG. 2A is a characteristic diagram showing the relationship between thecontent of Ni/(Ni+Co) in the films and the in-plane squareness of theplated films obtained from Example 10 and Comparative Example 7;

FIG. 2B is a characteristic diagram showing the relationship between thecontent of Ni/(Ni+Co) in the films and the in-plane coercive force ofthe plated films obtained from Example 10 and Comparative Example 7;

FIG. 3 is a cross sectional view of an example of a magnetic recordingmedium having alumite fine pores in which a magnetic member is filled byplating;

FIG. 4 shows the composition dependence of an in-plane residual magneticflux density, when Co-Fe or Co-Ni-Fe alloy is filled in alumite finepores. Note that the residual magnetic flux density is represented by aunit of kG.

DETAILED DESCRIPTION OF THE INVENTION

According to the first aspect of the present invention, the aboveproblems can be solved by providing a magnetic alumite film with anin-plane magnetic anisotropy.

An in-plane magnetic anisotropy film has an output spacing loss of -49.5dB when a recording wavelength is 0.5 micrometer and a spacing is 0.25micrometer, whereas a perpendicular magnetic anisotropy film has that of-60 to -90 dB. Under this condition, the in-plane magnetic anisotropyfilm has a reproducing output which is 3.3 to 106 times higher than thatof the perpendicular magnetic anisotropy film, and when a recordingwavelength is set to a given value of 0.5 micrometer and a spacing ismade greater than 0.25 micrometer, a difference between the reproducingoutputs thereof is more increased. From the above-mentioned, it ispossible that an ultra-high density recording greater than 500 kbpi canbe effected by perpendicular magnetic recording in principle in the caseof head/medium contact type recording, but the in-plane magneticanisotropy film is advantageously used as a medium in a medium/headnoncontact type magnetic recording system which is usually used at alinear recording density of 50 kbpi or less.

It has been reported that in-plane magnetic anisotropy was induced byfilling the fine pores of alumite anodized in a sulfuric acid bath withCoNi alloy (J. Electrochem. Soc., Vol. 122, No. 1, pp 32 (1975) Kawai etal). In the case of this medium, however, a ratio of an in-planeremanence to a perpendicular remanence (Mr∥/Mr⊥) was small in an amountof 2.5 and thus a substantial amount of a perpendicular magnetizationcomponent remains. When the Mr∥/Mr⊥ is less than 2.5, the reproducingoutput is greatly lowered because of the large spacing loss.

Further, in the case of the above publication, since a magnetic layerhas a large thickness of 1 micrometer, a magnetic head cannot effect asaturation recording, and further since a porosity of alumite is lessthan 0.1 and thus the saturation magnetization as a magnetic alumitefilm has a small value of about 60 emu/cc, sufficient reproducing outputcannot be provided.

To solve these problems, an alumite magnetic layer is made to athickness of 500 to 5000 angstroms and further a porosity is made to 0.1to 0.75 to decrease the perpendicular shape anisotropy, with a resultthat excellent in-plane magnetic characteristics having a Mr∥/Mr⊥ of 2.5or more are provided and a saturation magnetization can be increased to3.5 times that of the prior art. The upper limit value of the Mr∥/Mr⊥ isnot particularly specified, but it is generally about 20.

When the magnetic layer has a thickness exceeding 5000 angstroms, amagnetic head cannot effect a sufficient recording, whereas when it is500 angstroms or less, an absolute value of magnetization amount as amagnetic alumite film is made too small and thus a sufficientreproducing output cannot be provided. Porosity, when used herein, meansa ratio of pore area to cell area. A porosity greater than theconventional 0.06 can increase an amount of saturation magnetization ofa conventional magnetic alumite film. The upper limit of the porosity isconsidered to be about 0.75 (pore diameter=0.9×cell diameter), i.e.,when the pore diameter is 90% of the cell diameter, porosity will be0.75 when it exceeds this value, fine pores are partially connected toeach other, and thus the characteristic of the magnetic alumite film inwhich magnetic particles are separated by a nonmagnetic region(amorphous Al₂ O₃ l) is lost.

For example, a magnetic material mainly comprising Co or Fe is used as aferromagnetic material to be filled into alumite fine pores (e.g.,alumite anodized in sulfuric acid, oxalic acid, or phosphoric acid) andthus the large crystalline magnetic anisotropy of Co (Co single crystal:4.36×10⁶ erg/cc) is used together with the above decrease inperpendicular shape anisotropy.

For example, an addition of another element to Co or Fe can improve thein-plane magnetic characteristics. Elements to be added to Co or Fe maybe a magnetic member or a nonmagnetic member, that is, it may be anyelement as long as it induces in-plane magnetic anisotropy, and includesat least one element of, for example, P, S, B, Ni, Zn, Mn, Ag, Pb, Sn,W, Cu, Rh, Re, Pt, Pd, Au and the like and the hydroxides, oxides,phosphides, sulfides, and borides thereof.

These nonmagnetic additives must be soluble in a plating bath to be usedand be capable of being plated together with Co or Fe. The nonmagneticadditives can be independently used or two or more thereof can be usedin combination. In short, components necessary to provide desiredin-plane magnetic characteristics can be suitably selected and used.

According to the present invention, it was discovered by the inventorsthat a magnetic alumite film having in-plane magnetic anisotropy(magnetic film having an in-plane remanence greater than a perpendicularremanence) could be provided by the inclusion of the P element(phosphorus) in a magnetic material composed of a Co simple substance oralloy mainly composed of Co in alumite fine pores.

The alloy mainly composed of Co is an alloy including Co exceeding 50%,such as Co-Ni, Co-Fe, Co-Ni-Fe and the like.

In general, a content of P (phosphorus element) in the magnetic materialis preferably within a range from 0.05 to 33 at % and more preferablywithin a range from 2 to 10 at %. When a Co magnetic member filled inpores in alumite contains P within a range from 2 to 10 at %, a Coplated alumite film can be provided with strong in-plane magneticanisotropy.

Further, when a porosity of alumite (a ratio of the area of poresoccupied in a cell) is increased to 0.3 to 0.7 and an axial ratio ofCo-P particles is made to 0.5 to 10, the shape anisotropy of the Co-Pparticles can be reduced and the in-plane magnetic characteristics canbe more imporved.

A content of P in a Co or a Co magnetic alloy material is 33 at % orless, and a content thereof exceeding 33 at % is not preferable becauseit greatly reduces saturation magnetization and lowers a reproducingoutput. The lower limit of the content of P in the Co or Co magneticalloy member is not particularly specified, because even a slight amountof P added to Co has an effect to form an in-plane anisotropy film, butit is generally 0.05 at % or more.

In general, a content of P is preferably 2 to 10 at %, and an amountless than 2 at % is insufficient to further improve the in-planemagnetic characteristics and an amount exceeding 10 at % makes anin-plane coercive force greater than 1500 Oe and thus there is apossibility that a saturation recording cannot be effected.

On the other hand, a porosity of alumite is preferably 0.1 to 0.75 andan axial ratio of Co-P particles subsequently formed by filling of Co-Pferromagnetic material into alumite fine pores is preferably 0.5 to 10to lower shape anisotropy and further improve the in-plane magneticcharacteristics. An increase in the porosity also provides an effect forincreasing the saturation magnetization of the magnetic alumite film andis also advantageous to improve a reproducing output.

A content of Cu is preferably within a range from 0.05 to 50 at % andmore preferably within a range from 0.1 to 30 at %.

A content of other nonmagnetic members necessary to provide desiredin-plane magnetic characteristics can be suitably determined by a personskilled in the art experimentally.

An in-plane coercive force of the in-plane magnetization film ispreferably 500 to 1500 Oe. An in-plane coercive force less than 500 Oeis not enough for magnetic recording mediums, because demagnetizationeffects become large. Whereas, when an in-plane coercive force exceeds1500 Oe, sufficient recording cannot be effected by a magnetic head. Asdescribed above, in the magnetic alumite film according to the presentinvention, a longitudinal magnetic recording is made possible, reductionin the reproducing output is restricted with respect to a floatingamount of a magnetic head, and sufficient overwrite characteristics canbe expected.

Further, since respective magnetic particles subsequently formed byfilling the magnetic material into alumite fine pores are surrounded byaluminum oxide and perfectly separated, they are excellent in corrosionresistance and durability and further zigzag domains are difficult to begenerated in a magnetizing transition region. As a result, less noise isproduced in reproduction to permit a high reproducing output and a noisereduction is expected. In addition, since in-plane anisotropy directedto a particular direction is not produced (in-plane anisotropy magneticfield ˜50 Oe), no modulation arises in reproduction.

A phosphorus compound soluble in a Co plating bath is used as a sourcefor supplying the P element to be added to Co or Co alloy. Phosphite andhypophosphite in which a valence number of P is +3 or less such as, forexample, sodium phosphite (Na₂ HPO₃), sodium hypophosphite (NaPH₂ O₂)and the like are preferably used as the phosphorus compound. Phosphiteand hypophosphite can be used independently or in combination with twoor more types thereof. P having a valence number exceeding +3 is notmixed in Co. Therefore, phosphoric acid (H₃ PO₄) is not taken into Co inalumite fine pores, even if it is added to the Co plating bath. In thiscase, P has a valence number of +5 and the electron configuration of Pis the same that of Ne. Therefore, it is considered to be related to theabove phenomenon that P having a valence number of +5 is made stable andthus no electron is delivered in plating.

A content of the P element in the Co or Co magnetic alloy material canbe controlled by changing plating conditions such as a plating time,applied voltage, a pH, a bath temperature and the like in addition to aconcentration of a phosphorus compound to be added to a plating bath.

The above description with respect to the above P is also applicablesubstantially to Cu and other nonmagnetic members and low saturationmagnetization magnetic members, and they are supplied into aferromagnetic member by a compound soluble to a plating bath and acontent thereof is controlled by the same method as the case of the P.

Since sulfuric acid has a large dissociation constant and lowers anelectrical resistance of a bath, a voltage applied thereto is about ˜20V, when an anodic oxidation is effected, and a diameter of fine pores is˜200 angstroms. In contrast, sulfuric acid, oxalic acid and phosphoricacid have a small dissociation constant and thus a large voltage isapplied when an anodic oxidation is effected. Therefore, alumite havinga fine pore diameter of ˜500 angstroms can be obtained, and thus when amagnetic layer has the same thickness, alumite having an axial ratiohalf of that provided in the sulfuric acid bath can be obtained. Whenthe fine pores are enlarged in a bath of phosphoric acid, sulfamic acidor the like after the anodic oxidation has been effected, the axialratio can be further reduced.

Although the in-plane anisotropy film can be formed by the addition of Pand the control of the axial ratio as described above, other methods canbe also used.

For example, when Cr underlayers are filled in alumite fine pores andthe magnetic member according to the present invention is laminatedthereon, the surface (100) of the Co or Co alloy is preferably grown inparallel to a substrate and an easy axis of magnetization is oriented inthe substrate plane and thus a more excellent in-plane anisotropy filmcan be provided. The underlayer is not limited to Cr but may be anysubstance so long as it can orient the c axis of Co, parallel to thefilm plane.

A thickness of the underlayer is not particularly limited, but ingeneral, it is preferably within a range from 0.02 to 1 micrometer. Whenit is 0.02 micrometer or less, the surface (110) of Cr is notsufficiently grown and thus it is difficult to orient the c-axis of theCo or Co alloy parallel to the film surface, whereas when it exceeds 1micrometer, the effect applied to the in-plane orientation of the Co orCo alloy is saturated. Therefore, if the underlayer is made thicker than1 micrometer, it will be more uneconomical.

A depth of the fine pores formed in an alumite layer can be adjusted bycontrolling a time of anodic oxidation. Although it is not necessary todescribe, a depth of the fine pores is less than a thickness of thealumite layer.

Although the alumite layer can be directly formed on an aluminumsubstrate by anodic oxidation of the aluminum substrate, it can be alsoformed in such a manner that aluminum or aluminum alloy is deposited ona nonmagnetic substrate by a vapor deposition method and the vapordeposited layer is subjected to anodic oxidation. The vapor depositionmethod includes vacuum vapor deposition, ion plating, sputtering, ionbeam deposition, chemical vapor deposition (CVD) and the like.

A nonmagnetic substrate used in the magnetic recording medium of thepresent invention includes a polymer film such as polyimide,polyethylene terephthalate and the like, glasses, ceramics, anodizedaluminum, a metal plate such as brass and the like, a silicon singlecrystal plate, a silicon monocrystal plate the surface of which issubjected to a thermal oxidation treatment in addition to the aluminumsubstrate.

Further, the magnetic recording medium of the present invention includesvarious applications formed to enable them to be in sliding contact witha magnetic head, such as a magnetic tape and disk using as a substrate asynthetic resin film such as a polyester film, polyimide film and thelike and a magnetic disk and drum using as a substrate a disk and drumcomposed of an aluminum plate, glass plate and the like.

As described above, given stable magnetic characteristics, a lowanisotropy field in the film plane can be provided in the plane of amedium by using an in-plane magnetic anisotropy film which makes use ofalumite.

According to the second aspect, the magnetic recording medium of thepresent invention is provided with an in-plane magnetic anisotropy filmusing porous alumite.

The porous alumite has many fine pores in a direction perpendicular tothe film surface thereof (pore density: ˜5×10¹⁰ pores/cm²) and therespective pores are completely separated by amorphous Al₂ O₃. As aresult, a material which is filled in the fine pores and exhibitsin-plane magnetic anisotropy has a structure which is completelyseparated magnetically in the respective fine pores each other. Thus,the material exhibits perfect in-plane isotropic magneticcharacteristics regardless filling condition and fabrication apparatus.

Therefore, a given stable reproducing output can be provided in eitherdirection including circumferential or radial directions.

An apparent anisotropy filed in the film plane Hk in the magneticrecording medium of the present invention must be 100 Oe or less. Theterm "apparent" in this specification is used to represent a valuedetermined by the following equation based on an anisotropic energy inthe film plane obtained from the torque curve of a specimen beingrotated in a magnetic field while a uniform magnetic field parallel tothe film plane (˜15 KOe) is imposed.

    apparent anisotropy field Hk=2 Ku/Ms

where, Ms represents a saturation magnetization of the specimen. Whenthe apparent anisotropy field exceeds 100 Oe, a significant differencein magnetic characteristics is caused depending on the direction andlocation of the medium. As a result, a stable reproducing output cannotbe provided. An ideal value of Hk is zero and thus a lower limit is notspecified. In the state of Hk=0, perfect isotropic magneticcharacteristics can be provided in the film plane.

The apparent anisotropy is controlled to 100 Oe or less in such a mannerthat magnetic particles are perfectly separated by a nonmagnetic region,so that magnetic coupling of the magnetic particles does not arise.

As apparent from the following examples, according to the presentinvention, an excellent in-plane magnetization film can be provided bymaking an in-plane remanence 2.5 times or more of a perpendicularremanence, a thickness of a magnetic layer from 500 to 5000 angstroms, aporosity of alumite of from 0.1 to 0.75, and an in-plane coercive forcefrom 500 to 1500 Oe.

Next, the third aspect of the present invention will be described.

Conventionally, in the magnetic alumite film Fe has been used to form aperpendicularly magnetization film and thus it has been considered thatFe cannot be used for forming an in-plane magnetization film. It hasbeen discovered by the inventors, however, that when Fe is usedaccording to the following composition, i.e., (Co_(x) Ni_(1-x))_(1-y)Fe_(y) (0.5≦x≦1; 0<y≦0.3), even Co-Fe or Co-Ni-Fe alloy can be made intoan excellent in-plane magnetic film of high saturation magnetization.Note that the in-plane magnetization film according to the presentinvention means a magnetic film having an in-plane remanence greaterthan a perpendicular remanence.

Therefore, according to the magnetic alumite film of the presentinvention, longitudinal magnetic recording can be effected, a reductionin reproduction output is restricted with respect to a spacing loss, andsufficient overwrite characteristics are expected.

Further, since respective magnetic particles in the alumite aresurrounded by aluminum oxide and perfectly separated, the magneticalumite film is excellent in corrosion resistance and durability andfurther, since the magnetic coupling of the particles is not effected,zigzag domains are generated with difficulty in a magnetizing transitionregion. As a result, medium noise is restrained to permit a highreproducing output to be provided. In addition, since anisotropy fieldin the film plane is very small, no output modulation arises inreproduction.

With respect to the reason why the excellent in-plane magneticcharacteristics are realized, the inventors examined the mechanism whichgenerates the in-plane magnetic anisotropy using various measuring andanalyzing technologies. More specifically, the inventors investigatedshape anisotropy, magnetocrystalline anisotropy, magnetostrictioneffect, surface anisotropy, and induced magnetic anisotropy. While theinventors were not able to clearly identify the factor by which thein-plane magnetic anisotropy of the alumite film of the above alloy isgenerated, it is hypothesized that perhaps the above five magneticanisotropy generating factors integrally generate the in-plane magneticanisotropy.

FIG. 4 shows an example of the result of the measurement of the in-planeresidual magnetic flux density (Br) of the Co-Fe or Co-Ni-Fe platedalumite film according to the present invention. Note that the data wasmeasured under the condition of a porosity of 0.3. It is found from FIG.4 that a high in-plane residual magnetic flux density can be provided inthe range of 0.5≦x≦1 and 0<y≦0.3 of the alloy composition (Co_(x)Ni_(1-x))_(1-y) Fe_(y). Further, with respect to R/W characteristics, itis found that a reproducing output is substantially proportional to thein-plane residual magnetic flux density (Br), and when compared at themaximum values, the above alloy composition could provide an output atleast 40% higher than that of a substance composed of Co and Ni.

As described above, although the in-plane magnetization film can beformed by controlling the compositional ratio of Fe, other methods canbe also used in addition to it.

For example, when Cr underlayers are filled in fine pores of alumite andthe Co alloy according to the present invention is laminated thereon,the surface (100) of the Co alloy is grown in parallel to a substrateand an easy axis of magnetization is oriented in the film plane of thesubstrate and thus a more excellent in-plane magnetization film can beprovided.

A method of forming the in-plane magnetization film from a view point ofdecreasing perpendicular shape anisotropy by lowering an axial ratio offine pores of the alumite can also be used in addition to the abovemethod using the magnetocrystalline anisotropy of Co. A diameter of finepores of the alumite is substantially proportional to an electrolyticvoltage (V) when anode oxidation is effected, and the higher theelectrolytic voltage, the diameter of fine pores of the alumite isincreased. Therefore, as the diameter of the fine pores is increased,the axial ratio of magnetic particles in the pores (depth of finepores/diameter of fine pores) is lowered such that the depth of the finepores is kept constant, which is advantageous to create the in-planemagnetization film. As an example, it is desirable that the magneticparticles have an axial ratio of 30 or less and preferably 10 or less.

Sulfuric acid can be used to the anodic oxidation bath. Since sulfuricacid has a large dissociation and lowers the electric resistance of abath, a voltage applied thereto is about ˜20 V, when an anodic oxidationis effected, and a diameter of fine pores is ˜200 angstroms. In contrastto sulfuric acid, oxalic acid and phosphoric acid have a smalldissociation constant and thus a large voltage is applied when an anodicoxidation is effected. Therefore, alumite having a fine pore diameter of˜500 angstroms can be obtained, and thus when a magnetic layer has thesame thickness, alumite having an axial ratio half of that provided inthe sulfuric acid bath can be obtained. When the fine pores are enlargedin a bath of phosphoric acid, sulfamic acid or the like after the anodicoxidation has been effected, the axial ratio can be further reduced.

As described above, the magnetic alumite film can be made as an in-planefilm by the multiplied effect of the magnetocrystalline anisotropy dueto the existence of the underlayer and the decrease of perpendicularshape anisotropy due to the axial ratio, as desired, in addition to thecontrol of the compositional ratio of the Fe according to the presentinvention, so that the in-plane magnetization film having very excellentmagnetic characteristics can be provided.

A thickness of the underlayer is not particularly limited, but ingeneral, it is preferably within a range of from 0.02 to 1 micrometer.When it is 0.02 micrometer or less, the surface (110) of Cr is notsufficiently grown and thus it is difficult to longitudinally orient theeasy axis of magnetization of Co-Ni alloy, whereas when it exceeds 1micrometer, the effect applied to the longitudinal orientation of the Coalloy is saturated. Therefore, if the underlayer is made thicker than 1micrometer, it will be more 1 uneconomical. The underlayer is notlimited to Cr, but may be any substance so long as it can orient thec-axis of Co in plane direction of the film.

In general, the Co alloy magnetic layer of the magnetic recording mediumaccording to the present invention preferably has a thickness in a rangeof from 0.05 to 5 micrometers.

A depth of the fine pores formed in the alumite layer can be adjusted bycontrolling the time of anodic oxidation. Although it is not necessaryto describe, a depth of the fine pores is less than a thickness of thealumite layer.

According to the present invention, an in-plane magnetization film canbe formed even if Fe is contained as a component constituting magneticparticles, and further a reproducing output can be increased by theexistence of Fe.

PREFERRED EMBODIMENTS EXAMPLES

The present invention will be described below in detail with referenceto the examples.

Example 1

An aluminum substrate of a 2.5 inch size having a purity of 99.97% wascleaned and degreased in trichloroethane, the surface oxide layerthereof was removed in NaOH of 5 wt % at 50° C., and thereafter thesubstrate was neutralized in HNO₃ of 6 vol % at 20° C.

An anodic oxidation was effected in a bath containing H₂ SO₄ of 1 mol/land Al₂ (SO₄)₃ of 5 g/l at 18° C. with a constant voltage (counterelectrode: carbon) of 17.5 V to form an alumite layer of about 0.45micron meter. At the time, a cell diameter (Dc) and a pore diameter (Dp)of the alumite were 450 angstroms and 150 angstroms, respectively.Thereafter, the alumite was dipped in H₃ PO₄ of 1 wt % at 30° C. andthen the anodic oxidation was effected until a voltage across both theelectrodes reached 8 V (counter electrode: carbon) with a constantelectric current density of 40 mA/dm². Next, the alumite was dipped inthe bath for a predetermined period so that the pore diameter wasenlarged up to 380 angstroms.

Next, the alumite was transferred to a plating bath to be subjected to aCo-P plating. The bath was composed of Co²⁺ of 0.2 mol/l, H₃ BO₃ of 0.2mol/l, glycerine of 2 ml/l, and NaPH₂ O₂ of 0 to 0.02 mol/l with a pH of3 to 7 at 20° C., a power supply used for the plating was AC 500 Hz and16 Vp-p (counter electrode: carbon), and Co-P magnetic particles ofabout 1500 angstroms in height were filled by plating.

A specimen made by using NaPH₂ O₂ of 0.02 mol/l was cut off to 1 squarecentimeter, an external magnetic field of 16 KOe, which was parallel toa plane direction, was imposed thereon and the anisotropy in the filmplane was determined by a torque curve with a result that the anisotropyfield Hk in the film plane was 15 Oe.

Comparative Example 1

An aluminum substrate having a thickness of 1.28 mm with a Ni-P layerwas used as a nonmagnetic substrate and a 500 angstrom thick Co₈₀ Ni₂₀magnetic layer was formed on a Cr underlayer (thickness: 5000 angstroms)by a sputtering method. Then, an anisotropy in the film plane wasdetermined by the same method with a result that it was 830 Oe as Hk.

FIG. 1 shows how the in-plane magnetic characteristics (coercive forceand squareness) of the above specimen obtained from Example 1 and theCo-Ni sputtered film of the Comparative Example 1 were varied when thespecimens were rotated in an external magnetic field under the conditionthat the external magnetic field was applied in-plane direction of thefilm during rotation. In FIG. 1, an in-plane coercive force and anin-plane squareness are normalized by the maximum values of therespective specimens. The Co-P plated alumite film provides a constantin-plane coercive force and a constant in-plane squareness in anyrotation angle, but in the case of the CoNi sputtered film, an in-planecoercive force is reduced by 19.7% and an in-plane squareness is reducedby 9.8% in comparison with the maximum 1 values depending on angle.

It is understood from the fact that the in-plane magnetization filmusing alumite (in-plane coercive force: 700 Oe, in-plane squareness:0.64) exhibits good in-plane magnetic properties and their propertiesare almost independent of the measuring direction in-plane. So, themagnetic recording disk using this material exhibits little outputmodulation.

Example 2

The disk obtained from Example 1 was polished so that a Co-P magneticlayer was made to a thickness of 1 micron meter angstroms. Next, aperfluoropolyether lubricant was coated on the surface of the disk andR/W characteristics were evaluated. A magnetic head used was a Mn-Znferrite head with a track width of 16 micron meters, a gap length of 1.2micron meters, and the number of windings of 16+16, and a spacing was0.3 micron meter (linear speed: 8.13 m/s).

Table 1 shows various characteristics of the magnetic alumite films madein Example 1 and a Co-Ni plated magnetic alumite film prepared by Kawaiet al.

                  TABLE 1                                                         ______________________________________                                                Cell Dia.                                                                              Pore Dia. Magnetic Layer                                     Specimen                                                                              (Å)  (Å)   Thickness (μm)                                                                       Porosity                                 ______________________________________                                        (a)     450      270       0.15      0.33                                     (b)     450      270       0.15      0.33                                     (c)     450      380       0.15      0.64                                     (d)     450      380       0.15      0.64                                     (e)     450      380       0.15      0.64                                     (f)     450      380       0.15      0.64                                     (g)     450      380       0.15      0.64                                     Kawai et al                                                                           400      100       1.00      0.06                                     ______________________________________                                                pH of      P Content Mr/// Hc// Ms                                    Specimen                                                                              Plating Bath                                                                             (at %)    Mr.sup.1                                                                            (Oe) (emu/cc)                              ______________________________________                                        (a)     4          0         0.31   340 469                                   (b)     4          9.0       2.70  1040 426                                   (c)     4          0         10.90  350 909                                   (d)     3          10.8      3.60  1330 811                                   (e)     4          7.0       10.70  980 848                                   (f)     5          5.4       9.51   710 860                                   (g)     6          2.7       12.0   520 884                                   Kawai et al                                                                           6.5        0         2.4   1150  57                                   ______________________________________                                    

In Table 1, the specimen (a) to which Co simple substance was plated hasa saturation magnetization (Ms) greater than 57 emu/cc made by Kawai etal, but it has a Mr∥/Mr⊥ of 0.31 and a small Hc∥ of 340 Oe.

Specimen (c) has a pore diameter which was enlarged from 270 angstromsof Specimen (a) to 380 angstroms to achieve an improved in-planemagnetic anisotropy and saturation magnetization of Mr∥/Mr⊥=10.90 andMs=909 emu/cc, but has a small Hc∥ of 350 Oe.

On the other hand, Specimen (b) is the same as Specimen (a) with respectto configuration, but has P of 9.0 at % added to Co and thus the overallcharacteristics thereof are improved with Mr∥/Mr⊥=2.70, Hc∥=1040 Oe, andMs=426 emu/cc.

In the case of Specimens (d) to (g), P is added to Co and a contentthereof is changed in a range from 2.7 to 10.8 at % by changing a pH inthe plating bath in addition to the improvement in configuration similarto that of Specimen (c). Specimens (d) to (g) exhibit excellent in-planemagnetic characteristics in that Mr∥/Mr⊥ is 2.7 to 10.8, Hc∥ is 520 to1330 Oe and Ms is 811 to 884 emu/cc.

Table 2 shows the result of reproducing outputs at 4 KFCI of Specimens(b) and (d) to (g) shown in Table 1 and the Co-Ni plated alumite film ofKawai et al.

                  TABLE 2                                                         ______________________________________                                                     Reproducing Output                                                            at 4KFCI                                                         Specimen     (μVp-p/μm.m/s.Turn)                                        ______________________________________                                        (b)          0.049                                                            (d)          0.091                                                            (e)          0.098                                                            (f)          0.096                                                            (g)          0.103                                                            Kawai et al  0.020                                                            ______________________________________                                    

As apparent from the result shown in Table 2, the reproducing outputs ofthe Specimens (b) and (d) to (g) are 2.5 to 5.0 times the CoNi platedalumite film of Kawai et al. This is attributed to the result of themultiplied effects of the increase in Mr∥/Mr⊥, the reduction inthickness of the magnetic layer, and the increase in porosity of thealumite.

Example 3

An anodic oxidation was effected by the same method as that of Example 1using an aluminum substrate similar to that of Example 1 and an alumitehaving an alumite layer of 0.45 micron meter thick, a cell diameter of450 angstroms, and a pore diameter of 380 angstroms was made. Next, thealumite was transferred to a plating bath to be subjected to a Feplating. The bath was composed of Fe²⁺ of 0.2 mol/l, H₃ BO₃ of 0.2mol/l, glycerine of 2 ml/l with a pH of 3.0 (at 20° C.), and Feparticles of about 1500 angstroms in height were filled by plating usingAC 500 Hz and 16 Vp-p (counter electrode: carbon).

Example 4

An anodic oxidation was effected by the same method as that of Example 1using an aluminum substrate similar to that of Example 1 and an alumitehaving an alumite layer of 0.45 micron meter thick, a cell diameter of450 angstroms, and a pore diameter of 380 angstroms was made. Next, thealumite was transferred to a plating bath to be subjected to a Fe-Cuplating. The bath was composed of Fe²⁺ of 0.2 mol/l, Cu²⁺ of 0.002mol/l, H₃ BO₃ of 0.2 mol/l, glycerine of 2 ml/l with a pH of 3.0 (at 20°C.), and a multi-layered Fe/Cu particles of about 1500 angstroms inheight were filled in alumite pores by plating using a pulse waveformpower supply. Fe and Cu had an average thickness of 300 angstroms and 20angstroms, respectively.

Comparative Example 2

An anodic oxidation was effected by a method similar to that of Example1 using the same aluminum substrate as that of Example 1 except that thepore diameter enlarging treatment was not effected, and an alumitehaving an alumite layer of 0.45 micron meter thick, a cell diameter of450 angstroms, and a pore diameter of 150 angstroms was obtained. Next,the alumite was transferred to a plating bath similar to that of Example1 to fill the pores of the alumite with Fe of 1500 angstroms in height.

Example 5

The R/W characteristics of the disks made in Examples 3 and 4 andComparative Example 2 were evaluated by the same method as that ofExamples 1 and 2.

Table 3 shows the various characteristics of the magnetic alumite filmsmade by Examples 3 and 4 and Comparative Example 2.

                  TABLE 3                                                         ______________________________________                                                 Cell Dia.                                                                              Pore Dia. Magnetic Layer                                    Specimen (Å)  (Å)   Thickness (μm)                                                                       Porosity                                ______________________________________                                        Example 3                                                                              450      380       0.15      0.64                                    Example 4                                                                              450      380       0.15      0.64                                    Comparative                                                                            450      150       0.15      0.10                                    Example 2                                                                     ______________________________________                                                 pH of                                                                         Plating Cu Content        Hc// Ms                                    Specimen Bath    (at %)    Mr///Mr1                                                                              (Oe) (emu/cc)                              ______________________________________                                        Example 3                                                                              3       0         5.0     175  1100                                  Example 4                                                                              3       7.0       13.5    600  1000                                  Comparative                                                                            3       0         0.2     250   170                                  Example 2                                                                     ______________________________________                                    

As apparent from the result shown in Table 3, since the perpendicularshape anisotropy of Examples 3 and 4 was decreased by pore widening andby layer multiplication, the value of the Mr∥/Mr⊥ of the Examples 3 and4 was made to 10 times or more and the coercive force thereof was alsoimproved as compared with Comparative Example 2. In addition, the valuesof Ms of Examples 3 and 4 was increased to six times that of ComparativeExample 2 by the increase in the porosity.

Table 4 shows the reproducing outputs of Examples 3 and 4 andComparative Example 2 at 4 KFCI.

                  TABLE 4                                                         ______________________________________                                                     Reproducing Output                                                            at 4KFCI                                                         Specimen     (μV.sub.p-p /μm.m/s.Turn)                                  ______________________________________                                        Example 3    0.070                                                            Example 4    0.075                                                            Comparative  0.010                                                            Example 2                                                                     ______________________________________                                    

It is notified that the decrease of perpendicular shape anisotropy, andthe improvement of the Ms by the increase in the porosity contribute toincrease the reproducing output.

Example 6

An aluminum substrate having a purity of 99.99% (thickness: 65 micronmeters, 20 mm×20 mm) was subjected to an ultrasonic cleaning intorichloroethylene, the surface oxide layer thereof was removed in NaOHof 5 wt %, and thereafter the substrate was neutralized in HNO₃ of 6 vol% and washed with water. Next, anodic oxidation of the aluminumsubstrate was carried out in a bath (20° C.) of H₂ SO₄ of 1 mol/l usingcarbon as a counter electrode with a current density of 1 A/dm² to forman alumite layer of 0.3 micron meter thick. Thereafter, the diameter ofthe fine pores of the 1 alumite was enlarged to 270 angstroms in a bathof H₃ PO₄ of 1 wt % (30° C.). A Co-P plating bath was composed ofCoSO₄.7H₂ O of 0.2 mol/l, H₃ BO₃ of 0.2 mol/l, glycerine of 2 ml/l, andNaPH₂ O₂.H₂ O of 0.1 mol/l and a pH of the bath was adjusted to 4.0 byH₂ SO₄ of 1 mol/l. A power supply of AC 500 Hz and 6 V_(p-p) was usedfor the plating. The carbon was used as the counter electrode and theplating was effected for 3 minutes at 20° C.

Comparative Example 3

A Co plated film was formed by the same method as that of Example 6except that NaPH₂ O₂.H₂ O was not added to a plating bath.

Example 7

After an alumite layer having a thickness of 0.45 micron meter wasformed on a substrate by the same method as that of Example 6, thediameter of the fine pores of the alumite was enlarged to 370 angstromsin a bath containing phosphoric acid of 1 wt % at 30° C. Thereafter, thesubstrate was subjected to a CoNi-P plating by the following method. Aplating bath was composed of CoSO₄.7H₂ O of 0.090 mol/l, NiSO₄.6H₂ O of0.038 mol/l, H₃ BO₃ of 0.24 mol/l, glycerine of 2 ml/l, and NaPH₂ O₂.H₂O of 0.51 mol/l and a pH was adjusted to 6.5 by NaOH of 5 wt %. An ACpower supply of AC 500 Hz, 25 V_(p-p) was used for the plating, a DCbias was imposed so that -15 V was applied to an alumite side and +10 Vwas applied to a counter electrode (carbon) side, and the plating waseffected for 10 seconds at 20° C.

Comparative Example 4

A CoNi plated film was formed by the same method as that of Example 7except that a plating bath was composed of CoSO₄.7H₂ O of 0.064 mol/l,NiSO₄.6H₂ O of 0.064 mol/l, H₃ BO₃ of 0.24 mol/l, and glycerine of 2ml/l.

Example 8

After an alumite layer having a thickness of 0.3 micron meter was formedon a substrate by the same method as that of Example 6, the diameter ofthe fine pores of the alumite was enlarged to 370 angstroms in a bathcontaining phosphoric acid of 1 wt % at 30° C. Thereafter, a CoFe-Pplating was effected by the following method. A plating bath wascomposed of CoSO₄.7H₂ O of 0.090 mol/l, FeSO₄ (NH₄)₂ SO₄.6H₂ O of 0.006mol/l, H₃ BO₃ of 0.24 mol/l, glycerine of 2 ml/l, NaPH₂ O₂.H₂ O of 0.51mol/l and a pH was adjusted to 4.0 using H₂ SO₄ of 1 mol/l. An AC powersupply of AC 500 Hz and 25 V_(p-p) was used for the plating, a DC biaswas imposed so that -15 V was applied to an alumite side and +10 V wasapplied to a counter electrode (carbon) side, and the plating waseffected for 10 seconds at 20° C.

Comparative Example 5

A CoFe plated film was formed by the same method as that of Example 8except that NaPH₂ O₂, H₂ O was not added to a plating bath.

Example 9

After an alumite layer having a thickness of 0.3 micron meter was formedon a substrate by the same method as that of Example 6, the diameter ofthe fine pores of the alumite was enlarged to 370 angstroms in a bathcontaining phosphoric acid of 1 wt % at 30° C. Thereafter, a CoNiFe-Pplating was effected by the following method. A plating bath wascomposed of CoSO₄.7H₂ O of 0.085 mol/l, NiSO₄.6H₂ O of 0.036 mol/l,FeSO₄ (NH₄)₂ SO₄.6H₂ O of 0.007 mol/l, H₃ BO₃ of 0.24 mol/l, glycerineof 2 ml/l, and NaPH₂ O₂.H₂ O of 0.51 mol/l, and a pH was adjusted to 4.0using H₂ SO₄ of 1 mol/l. An AC power supply of AC 500 Hz and 25 V_(p-p)was used for the plating, a DC bias was imposed so that -15 V wasapplied to an alumite side and +10 V was applied to a counter electrode(carbon) side, and the plating was effected for 10 seconds at 20° C.

Comparative Example 6

A CoNiFe plated film was formed by the same method as that of Example 9except that NaPH₂ O₂.H₂ O was not added to a plating bath.

An in-plane coercive force and squareness of the magnetic alumite filmsobtained from the above Examples and Comparative Examples were measuredby a vibrating sample magnetometer with the maximum applied magneticfield of 10 KOe.

Table 5 summarizes the result of the measurement.

                  TABLE 5                                                         ______________________________________                                                                In-plane                                                        Film Composition                                                                            Coercive   In-plane                                   Specimen  (at %)        Force (Oe) Squareness                                 ______________________________________                                        Example 6 Co.sub.88.3 P.sub.11.7                                                                      1240       0.43                                       Comparative                                                                             Co.sub.100    440        0.14                                       Example 3                                                                     Example 7 Co.sub.77.8 Ni.sub.9.7 P.sub.12.5                                                           1000       0.45                                       Comparative                                                                             Co.sub.89.0 Ni.sub.11.0                                                                     550        0.27                                       Example 4                                                                     Example 8 Co.sub.84.3 Fe.sub.4.4 P.sub.11.3                                                           920        0.39                                       Comparative                                                                             Co.sub.95.0 Fe.sub.5.0                                                                      670        0.25                                       Example 5                                                                     Example 9 Co.sub.76.3 Ni.sub.8.5 Fe.sub.4.4 P.sub.10.7                                                1050       0.43                                       Comparative                                                                             Co.sub.85.7 Ni.sub.9.5 Fe.sub.4.8                                                           700        0.31                                       Example 6                                                                     ______________________________________                                    

As apparent from the result shown in Table 5, both the in-plane coerciveforce and squareness of the magnetic films were greatly improved byadding P into the ferromagnetic particles in the alumite pores.

Example 10

A CoNi-P plating was effected by the same method as that of Example 7except that, in the composition of the plating bath of Example 7,(CoSO₄.7H₂ O)+(NiSO₄.6H₂ O)=0.128 mol/l was kept unchanged and a ratioof Co²⁺ /(Co²⁺ +Ni²⁺) was changed.

Comparative Example 7

A CoNi plating was effected by the same method as that of ComparativeExample 4 except that, in the composition of the plating bath ofComparative Example 4, (CoSO₄.7H₂ O)+(NiSO₄.6H₂ O)=0.128 mol/l was keptunchanged and a ratio of Co²⁺ /(Co²⁺ +Ni²⁺) was changed.

FIGS. 2A and 2B show the relationship between the in-plane squarenessand coercive force of the magnetic alumite films obtained from Example10 and Comparative Example 7, and the ratio of atoms of Ni/(Ni+Co) inthe films. Note that in Example 10, a content of P, i.e., P/(Co+Ni+P) is0.092 to 0.135, and Comparative Example 7 does not contain P. Asapparent from FIG. 2, it is found that the P content causes the in-planesquareness and coercive force to be increased in the region where alarge amount of Co is contained. It is considered that the saturationmagnetization of the film is large at higher Co content, and theaddition of P contributes to the improvement of reproducing output.

Example 11

A Co-P plating was effected by the same method as that of Example 6except that the pH of a plating bath was adjusted to 6.5 by NaOH of 5 wt%.

Table 6 shows the result of the measurement of the in-plane coerciveforce and squareness of Co-P plated films obtained from Examples 6 and11.

                  TABLE 6                                                         ______________________________________                                                                              In-plane                                        Film Composition   In-plane Coercive                                                                        Square-                                 Specimen                                                                              (at %)       pH    Force (Oe) ness                                    ______________________________________                                        Example 6                                                                             Co.sub.88.3 P.sub.11.7                                                                     4.0   1240       0.43                                    Example 11                                                                            Co.sub.93.8 P.sub.6.2                                                                      6.5    900       0.28                                    ______________________________________                                    

As apparent from the result shown in Table 6, the increase of pH from4.0 to 6.5 causes the P content to be reduced and the in-plane magneticcharacteristics to be a little deteriorated, even if the composition ofthe plating bath is unchanged.

Example 12

An anodic oxidation of a rolled aluminum substrate of a purity of 99.99%was carried out in H₂ SO₄ of 1 mol/l at 20° C. with a constant electriccurrent density of 1 A/dm² to form an alumite layer of 0.45 micron meterthick. At the time, a cell diameter and a pore diameter were 450angstroms and 130 angstroms, respectively. Next, the specimens weredipped in a H₃ PO₄ of 1 wt % at 30° C. the pore diameter was enlarged to395 angstroms and homogenization of barrier layer was carried out.Thereafter, NaPH₂ O₂ of 0 to 0.2 mol/l was added to a basic plating bathcontaining CoSO₄ of 0.2 mol/l, H₃ BO₃ of 0.2 mol/l, and glycerine of 2ml/l, and a Co-P plating was effected at 20° C. with a pH of 4 using anAC power supply of AC 500 Hz and 16 V_(p-p). Table 7 shows variouscharacteristics of the thus obtained typical Co-P plated alumite films.

                  TABLE 7                                                         ______________________________________                                                          Specimen A Specimen B                                       ______________________________________                                        P Content (at %)  0          9.0                                              Cell Dia. (Å) 450        450                                              Pore Dia. (Å) 270        270                                              Magnetic Layer Thickness (Å)                                                                1450       2500                                             Axial Ratio       5.4        9.3                                              Porosity          0.33       0.33                                             S//               0.098      0.414                                            S⊥           0.313      0.235                                            Hc//(Oe)          340        1040                                             Hc⊥ (Oe)     1680       1350                                             S///S⊥       0.31       1.76                                             Ms (emu/cc)       470        430                                              ______________________________________                                                         Specimen C   Specimen D                                      ______________________________________                                        P Content (at %) 0            5.0                                             Cell Dia. (Å)                                                                              450          450                                             Pore Dia. (Å)                                                                              370          370                                             Magnetic Layer Thickness (Å)                                                               750          1400                                            Axial Ratio      2.0          3.8                                             Porosity         0.61         0.61                                            S//              0.667        0.580                                           S·5     0.061        0.054                                           Hc// (Oe)        340          680                                             Hc⊥ (Oe)    460          730                                             S///S⊥      10.9         10.7                                            Ms (emu/cc)      870          830                                             ______________________________________                                    

In Table 7, Specimens A and B exhibit the effect of the addition of Punder the condition that a pore diameter is 270 angstroms and a porosityis 0.33. Specimen A which does not contain P has a S∥/S⊥ of 0.31, thatis, this film is a perpendicular magnetization film. Whereas, Specimen Bwhich contains P of 9.0 at % has a S improved from 0.098 to 0.414 and aS∥/S⊥ of 1.76 and is moved to an in-plane magnetization film (S∥/S⊥>1)regardless that it has an axial ratio of about twice that of Specimen A.However, Specimen B has a large Hc of 1350 Oe, and thus it is consideredthat there still remains a perpendicular component.

Specimen C and D are used to examine the effect of the addition of P,when a porosity is increased from 0.33 to 0.61 and an axial ratio isreduced to 5 or less. Specimen C which does not contain P has asignificantly increased S⊥ of 0.667 but has a low in-plane coerciveforce of 340 Oe, whereas Specimen D which contains P of 5.0 at %exhibits an excellent in-plane magnetic characteristics with a S∥ of0.58, S∥/S⊥ of 10.7, and an Hc∥ of 680 and has a perpendicular coerciveforce reduced to about 700 Oe.

Example 13

A rolled aluminum substrate having a purity of 99.99% (3 cm×3 cm×65micron meters thick) was cleaned and degreased in trichloroethane and aanode oxidation was carried out in a bath containing H₂ SO₄ of 1 mol/land Al₂ (SO₄)₃ of 5 g/l at 18° C. with a constant voltage of 17.5 V toform an alumite layer of 0.45 micron meter thick. Next, the alumite wastransferred to H₃ PO₄ of 1 wt % and the anodic oxidation was againcarried out until a voltage across both electrodes (counter electrode:carbon) reached 8 V with a constant electric current density of 40mA/dm², and then the specimen was dipped in the bath to enlarge thediameter of the fine pores thereof.

Thereafter, the specimen was treated in the bath for 2 minutes with theconstant voltage of 8 V so that a barrier layer was homogenized.

Next, the specimen was transferred to a plating bath containing Co²⁺ of0.2 mol/l, Cu²⁺ of 0.002 mol/l, H₃ BO₃ of 0.2 mol/l, and glycerine of 2ml/l, and multi-layered Co/Cu particles of 0.25 micron meter in heightwere filled into the fine pores of the specimen by plating using a pulsewave power supply.

The basic idea of the pulse plating is an alternative application of anelectric potential (ECo) by which Co²⁺ is reduced and an electricpotential (ECu) by which Cu²⁺ is reduced.

Example 14

NaPH₂ O₂ having a concentration of 0.02 mol/l was added to the platingbath used in the Example 13 and a multi-layered Co₉₄ -P₆ /Cu particlesof 0.25 micron meter in height were filled into the fine pores of thealumite of Example 13 by plating.

Example 15

Fe²⁺ having a concentration of 0.2 mol/l was added to the plating bathused in the Example 13 and a multilayered Fe₆₀ -Co₄₀ /Cu particles of0.25 micron meter in height were filled into the fine pores of thealumite of Example 13 by plating.

Example 16

Cu²⁺ was removed from the plating bath used in Example 13 and Ni²⁺having a concentration of 0.1 mol/l was added thereto and amulti-layered Co/Ni particles of 0.25 micron meter in height were filledinto the fine pores of the alumite of Example 13 by plating.

Example 17

Cu²⁺ was removed from the plating bath used in Example 13 and Fe²⁺having a concentration of 0.2 mol/l was added thereto and a Fe/Cumulti-film of 0.25 micron meter was filled into the fine pores of thealumite of Example 13 by plating.

Comparative Example 8

The Co simple substance particles were filled into the fine pores of analumite under the same condition as that of Example 13 except that aplating bath did not contain Cu²⁺ and a power supply of AC 500 Hz and 16V_(p-p) was used.

Comparative Example 9

The Fe simple substance particles were filled into the fine pores of analumite under the same condition as that of Example 13 except that aplating bath did not contain Cu²⁺ and a power supply of AC 500 Hz and 16V_(p-p) was used.

Table 8 shows the configurational characteristics and magneticcharacteristics of the magnetic alumite films obtained in Examples 13 to17 and Comparative Example 8 and 9.

                  TABLE 8                                                         ______________________________________                                                  Cell Dia.                                                                              Pore Dia.                                                            (A)      (A)        Porosity                                                                             Mr///Ms                                  ______________________________________                                        Example 13                                                                              450      380        0.64   0.68                                     Example 14                                                                              450      380        0.64   0.74                                     Example 15                                                                              450      380        0.64   0.65                                     Example 16                                                                              450      380        0.64   0.70                                     Example 17                                                                              450      380        0.64   0.60                                     Comparative                                                                             450      380        0.64   0.64                                     Example 8                                                                     Comparative                                                                             450      380        0.64   0.32                                     Example 9                                                                     ______________________________________                                                 Hc//   Cu Layer Thickness                                                                          Ni Layer Thickness                                       (Oe)   (Å)       (Å)                                         ______________________________________                                        Example 13                                                                             520    200           --                                              Example 14                                                                             790    200           --                                              Example 15                                                                             600    200           --                                              Example 16                                                                             800    --            200                                             Example 17                                                                             500    200           --                                              Comparative                                                                            340    --            --                                              Example 8                                                                     Comparative                                                                            175    --            --                                              Example 9                                                                     ______________________________________                                    

As apparent from the result shown in Table 8, the provision of the layerstructure in the magnetic particles improves the in-plane squareness andcoercive force as compared with the cases in which plating was effectedonly by Co or Fe. From this result, it is considered that theintroduction of the multi-layered structure results in the effect oflowering the shape anisotropy of the particles.

The layered structure is not necessarily required to be a perfect layer.

Example 18

An aluminum substrate having a purity of 99.99% was cleaned bytrichloroethylene, and after the surface oxide layer thereof was removedin NaOH of 5 wt %, the substrate was neutralized in HNO₃ of 6 vol % andwashed with water. Next, an anodic oxidation of aluminum substrate wascarried out in a bath (20° C.) containing H₂ SO₄ of 1 mol/l using carbonas a counter electrode with a current density of 1 A/dm² to form analumite layer of 3 micron meter. Thereafter, the diameter of the finepores of the alumite was enlarged to 260 angstroms in a bath containingH₃ PO₄ of 1 wt % (30° C.). A plating bath was composed of H₃ BO₃ of 0.2mol/l, glycerine of 2 ml/l, and further a mixture prepared by CoSO₄.7H₂O, FeSO₃ (NH₄)₂ SO₄.6H₂ O, and NiSO₄.6H₂ O to provide a desired alloycompositional ratio. A pH of the bath was adjusted to 3 by H₂ SO₄ of 1mol/l. A power supply of AC 500 Hz and 16 V_(p-p) was used for platingand the plating was continued using carbon as a counter electrode at 20°C. until overflow occurred. Several kinds of the thus formed magneticalumite films were polished to reduce a thickness of the magnetic layerthereof to 0.7 micron meter, and the recording characteristics thereofwere evaluated under the following conditions. A used magnetic head wasa metal-in-gap (MIG) type ring head having a CoNbZr amorphous layer(Bs9000G) sputtered to the vicinity of the gap thereof and had a gaplength of 0.44 micron meter. A spacing between the magnetic head and arecording medium in the evaluation was 0.22+0.1 micron meter, and theperformance of various mediums were compared based on an output at arecording density of 10 KFCI. Table 9 summarizes the composition of theprepared specimens and the result of the measurement of the in-planeresidual magnetic flux density Br (kG) and the reproducing outputthereof at a recording density of 10 KFCI. Note that, in Table 9, thereproducing output of Specimen composed of Co₇₀ Ni₃₀ is used as areference to the reproducing outputs.

                  TABLE 9                                                         ______________________________________                                                          In-plane Residual                                                             Magnetic Flux                                                                              Reproducing Output                             Specimen                                                                             Composition                                                                              Density (kG) at 10 KFCI (dB)                                ______________________________________                                        A      Co.sub.70 Ni.sub.30                                                                      1.5          0.0                                            B      Co.sub.70 Ni.sub.20 Fe.sub.10                                                            2.2          +3.3                                           C      Co.sub.50 Ni.sub.48 Fe.sub.2                                                             1.9          +2.0                                           D      Co.sub.70 Fe.sub.30                                                                      1.8          +1.5                                           E      Co.sub.25 Ni.sub.46 Fe.sub.29                                                            1.1          -2.7                                           F      Co.sub.100 1.0          -3.5                                           ______________________________________                                    

As apparent from the result shown in Table 9, the medium according tothe present invention satisfying the condition of 0.5≦x≦1 and 0<y≦0.3 inthe composition of (Co_(x) Ni_(1-x))_(1-y) Fe_(y) forms an in-planemagnetization film of high saturation magnetization and thus can improvethe reproducing output thereof.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

Claimed is:
 1. A magnetic recording medium comprising an aluminum oraluminum alloy substrate and a magnetic alumite layer formed on saidsubstrate, said magnetic alumite layer, formed by anodic oxidation ofsaid aluminum or aluminum alloy, comprising fine pores filled with aferromagnetic material to provide said magnetic layer in a discreteform, said magnetic alumite layer having an in-plane remanence at least3.6 times greater than a perpendicular remanence, said ferromagneticmaterial being selected from at least one member of the group consistingof Co containing P, and a Co alloy containing P, content of said P insaid ferromagnetic material being within a range of from 0.05 at % to 33at %, said magnetic alumite layer having a thickness of from 500 to 5000angstroms, said alumite layer having a porosity of from 0.1 to 0.75 andsaid recording medium having an in-plane coercive force of from 500 to1500 Oe.
 2. A magnetic recording medium according to claim 1, whereinsaid ferromagnetic material filled in said fine pores by platingcomprises Co-P having an axial ratio within a range of from 0.5 to 10.3. A magnetic recording medium according to claim 1, wherein saidmagnetic alumite layer is an in-plane magnetic anisotropy film formed onsaid substrate, wherein the anisotropy magnetic field in said film planeis 100 Oe or less.
 4. A magnetic recording medium comprising an aluminumor aluminum alloy substrate and a magnetic alumite layer formed on saidsubstrate, said magnetic alumite layer, formed by anodic oxidation ofsaid aluminum or aluminum alloy, comprising fine pores filled with aferromagnetic material and a non-magnetic material or a magneticmaterial having a low saturation magnetization less than that of saidferromagnetic materials said ferromagnetic material being selected fromat least one member of the group consisting of a Co containing P, and aCo alloy containing P, said magnetic layer having a thickness of from500 to 5000 angstroms, said alumite layer having a porosity of from 0.1to 0.75 and said recording medium having an in-plane coercive force from500 to 1500 Oe, wherein said ferromagnetic material is filled in saidfine pores in a long axis direction thereof alternately with saidnon-magnetic material or said magnetic material having a low saturationmagnetization less than that of said ferromagnetic material to form adiscrete layered structure, having an in-plane remanence Mr∥ at least3.6 times greater than a perpendicular remanence Mr⊥ .
 5. A magneticrecording medium according to claim 4, wherein the content of said P insaid ferromagnetic material is within a range of from 0.05 at % to 33 at%.
 6. A magnetic recording medium according to claim 1, wherein saidferromagnetic material is a cobalt alloy containing P selected from thegroup consisting of Co-Ni, Co-Fe, and Co-Ni-Fe.
 7. A magnetic recordingmedium according to claim 3, wherein said magnetic recording medium is arigid disk.
 8. A magnetic recording medium according to claim 5, whereinthe content of said P is within a range of from 2 to 10 at %.